Animal activists were taken away by police after running on to the track at Epsom before the Cazoo Derby.
Pro-vegan climate group Animal Rebellion claimed six women entered the area wearing sashes reading “Animal Justice” just before the premier Classic at 4.30pm.
It comes after activists from the same group entered the ceremonial route on The Mall before Trooping the Colour, later being arrested by police on Thursday.
The women could be seen falling to the floor as the police moved in on them on Saturday.
Dozens of officers were working to move them, as the Princess Royal and her family watched on.
The Queen’s daughter Anne was there alongside husband Vice Admiral Sir Tim Laurence and children Peter Phillips and Zara Tindall, who was with husband, former rugby player Mike.
The crowds cheered as the activists were taken away, with a voice on a Tannoy apologising to spectators.
The group said the protest was aimed at making “a definitive statement, and act, against the cruelty and harm the horseracing industry represents”.
Orla Coghlan, one of those there, said: “Horseracing took the lives of 220 animals on racecourses in the UK last year, and this is just the tip of the iceberg.
“In this country, over a billion land animals are killed for food each year. Exploitation of, and violence against, animals is fuelling the climate emergency and suffering across the globe.
“It is obvious we must choose life over death and stop animal exploitation.”
A spokesperson for the group said: “Whether it’s horseracing, dairy, or the meat industry, animal exploitation has no part in our world.”
Surrey Police has been approached for comment.